1. Field of the Invention:
This invention relates to a fluid-damping vibration-isolating device for supporting or bearing vibrating bodies like automobile engines in a vibration-isolating manner.
2. Description of the Related Art:
In supporting engines suspended on motor car vehicles in a vibration-insulatingmanner, a vibration-isolating support device is required to meet two requirements, one of which is that damping rate is large against high-amplitude, low frequency oscillations generated at low speed and the other of which is that vibration insulating property is large against high frequency oscillations generated at high speed. However, vibrations of automobile vehicles due to low frequency oscillations and middle frequency oscillations such as cranking oscillation, idling oscillation and noises due to high frequency oscillations such as confined or muffled sound, transmission sound are contradictory to each other in property, and consequently, it is difficult to satisfy vibration-insulating performance against both properties efficiently and simultaneously.
Recently, fluid-damping vibration-isolating support devices have been adopted that allow their damping function to be shared by sealed liquid and their vibration-insulating function to be shared by a vibration-isolating base member made of a rubber elastomer which constitutes a wall of a chamber for the sealed liquid.
Prior art vibration-isolating support devices of this type are of a well-known construction in which the internal chamber defined in a main support body having a vibration-isolating base member formed of a rubber cylindrical body of divided into two chambers by means of a partition plate and the two chambers are put in communication with each other through an orifice provided in the partition plate and sealed with a liquid therein. As the partition plate, most of a prevailing ones are made of a high-rigidity material and fixed to the internal wall of the main support body in the periphery thereof.
There are further proposed support devices provided with another partition plate which is constructed of a thin film-like plate so that small amplitude vibrations in the high frequency region are easily accommodated, and some are furnished for actual use.
The former type of known devices stated above have, however, difficulties in that in the high frequency vibration region, hydraulic pressure of the liquid chamber is elevated and dynamic spring rate becomes large because of the high rigidity property and the fixed structure of the partition plate. As a consequence, confined or muffled sound is generated, impairing quietness of a car room.
On the other hand, the latter type of devices are disadvantageous in that damping properties decline against middle frequency and low frequency vibrations, and further have the problem that it is difficult to make partition plates of a diaphragm structure that have a uniform thickness and constant reliable qualities in respect of mechanical strength and properties.
Accordingly, this invention is designed for solving the drawbacks prior art support devices as stated above have. That is, a primary object of this invention is to suppress the rise of hydraulic pressure due to high frequency oscillations as well as to exhibit damping action against low frequency oscillations, thereby to avoid generation of confined sound, by using, as a member which allows the orifice to exhibit effectively damping performance against low frequency oscillations, a partition plate formed of a separator member having at least one through-hole in its inner flat plate portion and an orifice in its outer peripheral thick wall portion and of a stopper member which is capable of closing the through-hole upon low frequency oscillation and of putting the through-hole in communication upon high frequency oscillation, whereby to contribute to commercialization of motor vehicles of low vibrations and low noises.